An automotive body is generally formed of structural members mainly including vehicle longitudinal members that are disposed along a vehicle longitudinal direction and vehicle widthwise members that are disposed along a vehicle widthwise direction. The structural members such as vehicle longitudinal members and vehicle widthwise members, each of which is connected to other members by a flange that is formed at either end of each structural member, ensure the rigidity required for the automotive body, and bear the load.
The structural member for the automotive body requires, for example, a high deformation tolerance against the load acting along the axial direction of the structural member, and a high torsional rigidity. A thinner high-tensile steel sheet having high strength, for example, high tensile strength (high-strength steel sheet or high tensile strength steel sheet), has been increasingly used in recent years as a material for such a structural member in an aim to reduce automotive body weight and improve collision safety. For heavy automobiles such as trucks, however, structural members made of steel sheets of large thickness may be used.
For example, a floor cross member, which is used as a structural member to reinforce a floor of an automotive body, has a cross section substantially shaped like a gutter and is connected to side sills or other vehicle longitudinal members via outward flanges formed at both ends of the floor cross member. It is important for such a floor cross member to have an increased bonding strength with other members and an increased torsional rigidity to ensure the automotive body rigidity and better load transfer property in a case where an impact load is applied.
Patent Literatures 1 to 3 disclose manufacturing methods for structural members for automotive bodies to eliminate defects in the shape fixation of press formed products using high strength materials by getting creative with pad mechanisms used in dies. The manufacturing methods described in these Patent Literatures have attempted to improve in shape fixability after press forming by intentionally generating deflection of a material during forming depending on the positional relationship between the top of a punch and a flat pad of only a part that faces a flat part of the top of the punch.
Further, Patent Literature 4 discloses a flange-shaping die for shaping a flange in an end of a panel product for an automotive body. The flange shaping die can shape a center flange continuing to a center wall and a sideward-protruding flange continuing to a side wall by using the same die in one-time step. Patent Literature 4 also discloses an example in which a blank material is folded while a portion of the blank material to be formed into the center wall is held by a pad.